1. Field of the Invention
The present invention relates to a power generating system containing a power generator to generate power utilizing energy on the outside of the system, especially relating to a power generating system to drive load means (electronic equipment and the like) efficiently utilizing electric energy generated even when the polarity of generated voltage of the power generator is reversed according to the circumstances.
2. Description of the Related Art
There exits a power generating system which self-contains a power generator which converts outside energy such as light energy, thermal energy, or mechanical energy into electric energy, and is able to utilize the electric energy generated by the power generator for driving electronic equipment.
As such a power generating system, a solar battery system in which a solar battery is used as the power generator, a mechanical power generating system which is a means for utilizing mechanical energy of a rotating weight by converting into electric energy, or a power generating system by temperature difference which is a means for generating power with thermal energy caused by a temperature difference on both sides of a plurality of thermocouples connected in series, can be cited.
Particularly, as an example of the conventional power generating systems of those described above, there exists a power generating (thermoelectric) system by temperature difference which applies to an electronic timepiece, which is typically a compact portable electronic equipment, as shown in FIG. 7.
In the electronic timepiece of this thermoelectric system, a power generator 10 is connected to a load means 20 which consists of an accumulator 22 and a timekeeping means 21 through a switch means 30, and is configured to be able to utilize the generated power from the power generator 10 in the load means 20. That is, in this example, a current generated by the generated voltage of the power generator 10 is rectified by the switch means 30, and the rectified current is outputted to the accumulator 22 and the timekeeping means 21 to charge the accumulator 22 and to drive the timekeeping means 21.
The power generator 10 consists of plural thermocouples (not shown) connected in series. The power generator 10, for example this thermoelectric system, used to drive the electronic timepiece, is arranged in a manner that a warm junction side is contacted with a case back of the timepiece while a cold junction side is contacted with a case which is thermally insulated from the case back. Through this arrangement, thermal energy created by a temperature difference between the case cooled by outside air and the case back heated while the timepiece is worn by bodily temperature, is converted into electric energy to generate power, and the load means including the timekeeping means is driven by the generated electric power.
The load means 20 is configured to connect in parallel the timekeeping means 21, which has a time-keep function, with the accumulator 22 that is a second battery. The timekeeping means 21 grounds its positive pole terminal and connects its negative pole terminal to the switch means 30 as a negative pole of the load means 20.
The switch means 30 consists of first to fourth diodes 36 to 39, and connects these diodes in a bridge-shape so as to form a so-called full-wave rectifier. That is, one end of the power generator 10 connects to an anode of the first diode 36 and a cathode of the fourth diode 39, and the other end of the power generator 10 connects to an anode of the second diode 37 and a cathode of the third diode 38.
An anode of the third diode 38 and an anode of the fourth diode 39 are connected to a negative pole of the load means 20, and a cathode of the first diode 36 and a cathode of the second diode 37 are grounded.
The power generator which consists of a thermocouple (thermoelement) in this sort of the thermoelectric system, has a property in which the polarity of the generated voltage is changed by a direction of the temperature difference given from the outside of the thermoelectric system. Accordingly, in the power generator in the thermoelectric system, the polarity of the generated voltage reverses in accordance with a change of circumstances.
For instance, when the above-described electronic timepiece is a wrist watch which is attached to an arm, usually the temperature on the case back side which is closely contacted with the arm is higher than that on the case side which is exposed to the outside air, however, when the wrist watch is used in direct sunlight in the middle of summer, in a high temperature working circumstance, or in a torrid zone, it may happen that the case side is higher in temperature than the case back side. As a result, the polarity of the generated voltage created by the power generator 10 is sometimes reversed.
The switch means 30 in FIG. 7 is provided to make effective use of the generated power even when the polarity of the generated voltage created by the power generator 10 is reversed as described above.
However, in order to obtain generated voltage of about 1.0V required to operate the electronic timepiece from the power generator 10 by means of a slight temperature difference created in the inside of a timepiece, more than two thousand thermocouples are required to be connected to the power generator 10 in series. When such a power generator is attempted to be constructed in a limited space like a timepiece, the internal resistance of the thermocouples becomes at least of the magnitude of several tens of K .OMEGA.. Accordingly, even when a bridge rectifier circuit of the switch means 30 as shown in FIG. 7 is configured with the Schottky barrier diode and the like, current is difficult to generate, and the electric power which can be taken out to the load means 20 side is only 40% as much as the amount of power originally expected. This brings a disadvantage that the utilization efficiency is very poor.